Study finds amoeba 'grazing,' killing bacteria usually protected by film

Mitchell Nitschke, a research specialist from Sussex Wisconsin, examines amoeba on a new microscope in the Filutowicz lab. Dictys grow fast enough to be seen in real time. Credit: David Tenenbaum, University Communications

Bacteria have developed an uncountable number of chemistries, lifestyles, attacks and defenses through 2.5 billion years of evolution. One of the most impressive defenses is biofilm—a community of bacteria enmeshed in a matrix that protects against single-celled predators and antibiotics—chemicals evolved by competitors through the course of evolution, including other bacteria and fungi.

Now, a University of Wisconsin-Madison professor of bacteriology has shown the first proof that a certain group of amoeba called dictyostelids can penetrate biofilms and eat the bacteria within. "This is the first demonstration that dicty are able to feed on biofilm-enmeshed bacteria," Marcin Filutowicz says.

In an article now online in the journal Protist, Filutowicz, first author Dean Sanders of the Wisconsin Institute for Discovery, and colleagues show time-lapse, microscopic movies proving the amoeba's voracious appetite for five species of bacteria. In the study, the researchers pitted four types of amoeba called dictyostelium (dictys) against biofilm-forming bacteria that harm plants or humans. The target bacteria included:

Pseudomonas aeruginosa, a common, multi-drug resistant bacteria that afflicts people who have, for example, burns or cystic fibrosis;

Pseudomonas syringae, pathogen of beans;

Klebsiella oxytoca, cause of colitis and sepsis; and

Erwinia amylovora, cause of fire blight in apples and pears.

As expected, the results depended on the strain of dicty and species of bacteria; in several cases, the dictys completely obliterated a thriving biofilm containing millions of bacteria within a day or two. The study, Filutowicz says, "contains the first movies ever to show dicty cells moving into a biofilm and devouring the bacteria." Because they form a multi-cellular phase sometimes called a "slug," dictys are sometimes called "social amoeba."

Beyond the visual evidence, spore germination and the subsequent union of single-celled dictys into a multi-cellular "slug" both showed successful attacks against all four species of bacteria.

Filutowicz became interested in dictys after discovering a neglected archive of about 1,800 strains amassed by Kenneth Raper, a bacteriology colleague who started collecting the soil-borne microbes around the world in the 1930s. "Raper was the first to isolate dictys, but after he died, his life work was scattered around the department and neglected," Filutowicz says.

Filutowicz was intrigued, but he knew very little about dictys. Then, the answer to his most fundamental question—"How do I grow them?" triggered a mental chain reaction. He found that Raper and his followers were feeding and growing dictys in the lab using bacterial prey, but nobody had apparently pursued their real-world potential as microbe hunters. "If you grow them on E coli [a common resident of the human intestine], I quickly realized, because dictys are not pathogenic, we might use them as a biological weapon against bacteria."

Having previously started Conjugon, a company devoted to developing benign bacteria to defeat pathogenic microbes, Filutowicz says he was "attuned to biological approaches, which were unheard then, and so this idea fell on a very fertile mind."

With bacteria becoming resistant to a growing number of antibiotics, that's welcome news, although using a living organism may add complexity to the task of getting regulatory approval.

Since 2010, Filutowicz has learned a good deal about how dicty "graze" upon bacteria, and which ones they prefer. "We looked at how these cells dismantle biofilms, trying to understand what physical, chemical and mechanical forces deconstruct the biofilms, and how the dictys move in 3-D space. These are phagocytes, and they behave much like our own immune cells," says Filutowicz.

His collaborator, Curtis Brandt, a professor of ophthalmology and visual science at UW-Madison, has produced promising results suggesting that the organisms are harmless to rodents, and is preparing to use dictys to fight bacterial keratitis, an eye infection, first in rodents and then in humans, in research supported by the National Institutes of Health.

"This medical application may not reach the clinic in my lifetime, but it has a lot of promise, and eventually we may be able to advance it in many other medical uses," Filutowicz says.

In 2010, Filutowicz formed Amoebagone, to advance research into use of dictys, starting by trying to fight fire blight and other bacterial infections of fruit trees and vegetables; supported by the National Science Foundation.

Between the far-off human medical potential, and the near-term use in agriculture, Filutowicz is delightedly pulling on the thread left by Ken Raper's beneficial microbes; licensed by the Wisconsin Alumni Research Foundation to AmoebaGone.

"To make a discovery, it needs some level of naiveté," he says. "If you know too much, you immediately appreciate why things will not work, cannot work. Otherwise, if it was a good idea, people would have done it already. Colleagues said dictys behaved like human phagocytes, but they never mentioned harnessing them as biological controls. Every day I walk through the departmental hallway and read the inscription: "Discovery consists of seeing of what everybody has seen and thinking what nobody has thought. I was lucky enough to enter this as the foolish innocent."

Related Stories

Bacteria are a cunning foe; at a worrisome rate, they are developing resistance to the current arsenal of antibiotic drugs. Without new drugs, society may be approaching a world reminiscent of the pre-antibiotic era, when ...

New research from the University of Copenhagen reveals that bacteria which agglutinate before entering the body are far more resistant than single-celled bacteria. This may be the cause of chronic infections.

A failed experiment turned out to be anything but for bacteriologist Marcin Filutowicz. As he was puzzling out why what should have been a routine procedure wouldn't work, he made a discovery that led to the creation of a ...

(Medical Xpress) -- Bacteriologist Marcin Filutowicz specializes in developing antimicrobial technologies that one day may help replace antibioticsand save livesas the power of our antibiotics arsenal wanes. But ...

In 2011 the Queller-Strassmann lab, then at Rice University, made a startling announcement in Nature Letters. They had been collecting single-celled amoebae of the species Dictyostelium discoideum from the soil in Virginia ...

Recommended for you

Researchers at North Carolina State University have for the first time identified a specific chemical used by the higher termite castes—the queens and the kings—to communicate their royal status with worker termites. ...

Working with light and genetically engineered bacteria, researchers from Stanford University are able to shape the growth of bacterial communities. From polka dots to stripes to circuits, they can render intricate designs ...

Bacteria and Archaea are two of the three domains of life. Both must have evolved from the putative last universal common ancestor (LUCA). One hypothesis is that this happened because the cell membrane in LUCA was an unstable ...

Researchers at the University of British Columbia have shed new light on how mountain pine beetles produce an important pheromone called trans-verbenol, which could aid in efforts to better predict outbreaks.

It's been nearly two decades since a UC Santa Cruz research team announced that they had assembled and posted the first human genome sequence on the internet. Despite the passage of time, enormous gaps remain in our genomic ...

Death is certain for all living things, including the body's cells. The act of dying is in fact as sophisticated as any process a cell might perform during its lifetime—and when glitches in cell death occur, they can lead ...

0 comments

Please sign in to add a comment.
Registration is free, and takes less than a minute.
Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.